Drum for magnetic separator and relevant production method

Abstract

In a drum for magnetic separator comprising a cylinder (C) of ferromagnetic material on the outside of which there are formed a plurality of longitudinal grooves ( 6 ) housing permanent magnets ( 7 ) arranged in longitudinal rows along a magnetic arc of 130°-160° with alternate N-S polarity, the cylinder (C) being located within a shell (M) of nonmagnetic material, the length (D) of the single dipole of the magnetic circuit is comprised in a range between 100 and 150 mm so as to provide a substantially homogeneous magnetic field along the whole magnetic arc, thanks to the limited length (D) of the dipole which results in a sinusoidal pattern of very limited amplitude and therefore with nominal values of the magnetic field that are present over almost 100% of the magnetic arc.

The invention claimed is: 
     
       1. Drum for magnetic separator comprising a cylinder (C) of ferromagnetic material closed at its ends by two flanges having central hubs provided with seats for bearings and locking clamps, said central hubs being arranged along the longitudinal axis (A-A) of said cylinder (C), a plurality of longitudinal grooves being formed on the outside of the cylinder (C) and housing permanent magnets arranged in longitudinal rows of a single polarity along a magnetic arc of about 130° to 160° with alternate N-S polarity between adjacent rows, the cylinder (C) being located within a shell (M) of non-magnetic material closed at its ends by two flanges (F) having flanged hubs (MF) provided with seats for said bearings, at least one of said flanged hubs (MF) being also provided with means for receiving from a motor the motion to drive into rotation said shell (M), wherein the length (D) of the single dipole of the magnetic circuit is in a range between 100 and 150 mm. 
     
     
       2. Drum according to  claim 1 , wherein the magnets are all identical and the magnets are housed in progressively deeper longitudinal grooves in a release zone at the end of the magnetic arc. 
     
     
       3. Drum according to  claim 1 , further comprising a plurality of rotatable ball supports arranged in a chequered pattern among the magnets, the balls of said supports projecting by 0.3-0.4 mm with respect to the active surface of the magnets. 
     
     
       4. Drum according to  claim 3 , wherein the play (G) between the active surface of the magnets and the internal surface of the shell (M) is ≦2 mm. 
     
     
       5. Drum according to  claim 1 , wherein the external surface of the shell (M) is coated with an epoxy paint that forms a high-friction layer. 
     
     
       6. Drum according to  claim 1 , wherein an arm (B) for adjusting the position of the magnetic arc of the cylinder (C) is secured to one of the hubs. 
     
     
       7. Drum according to  claim 1 , wherein the magnets are made of a Nd—Fe—B alloy. 
     
     
       8. Drum according to  claim 1 , wherein the shell (M) is made of AISI 316 stainless steel having a thickness (Sm) of 4 mm. 
     
     
       9. Method for producing a drum for magnetic separator according to  claim 1 , comprising:
 a) welding the closure flanges at the ends of the cylinder (C); 
 b) fixing the hubs at the center of the flanges; 
 c) machining the cylinder (C) on a lathe to achieve perfect coaxiality of the hubs with the outside of the cylinder (C) and to form on the hubs the seats for the bearings and for the locking clamps; 
 d) milling the longitudinal grooves on the outside of the cylinder (C); 
 e) fixing the magnets into the grooves; and 
 f) introducing the cylinder (C) inside the shell (M) and sealingly mounting the closure flanges (F) of the latter; 
 
       wherein in step d) the grooves are formed at a distance such that the length of the single dipole of the magnetic circuit is in a range between 100 and 150 mm. 
     
     
       10. Method according to  claim 9 , wherein in step d) there are also formed seats for ball supports ( 8 ) which are subsequently fixed in said seats so as to project by 0.3-0.4 mm with respect to the magnets. 
     
     
       11. Method according to  claim 10 , wherein in step e) there are also fixed easily removable plugs into the seats for the ball supports and further includes the following steps between steps e) and f):
 e′) covering the region of the cylinder (C) where the magnets are present with a wrapper sealed with a putty suitable to allow the filling of said wrapper with an epoxy resin; 
 e″) filling the wrapper with an epoxy resin and subsequently removing the wrapper upon hardening of the epoxy resin; 
 e′″) machining the cylinder (C) on a lathe to perform the grinding at the desired diametral size of the surface covered with magnets and of the interspaces filled with resin; 
 e″″) removing the plugs and fixing the ball supports. 
 
     
     
       12. The drum of  claim 1 , wherein the means for receiving from a motor the motion to drive into rotation said shell is a toothed wheel (R). 
     
     
       13. The drum of  claim 1 , wherein the length (D) of the single dipole of the magnetic circuit is 127 mm.